Premium tubular threaded joint comprising at least a threaded element with end lip

ABSTRACT

The premium threaded tubular connection comprises, on at least one threaded element, a distal abutment surface ( 7 ) at the free end of a threaded element and a lip sealing surface ( 5 ) at a given distance from the threading.  
     The lip comprises an appendix ( 13 ) which extends the lip towards its free end beyond the lip sealing surface ( 5 ) so that the lip has both high radial stiffness and low axial stiffness.  
     This results in enhanced performance as regards the seal of the threaded connection under pressure and/or under tension, and in other advantages (precision of real makeup torque, mechanical strength in axial compression, a shock barrier effect, tolerance in engaging the threaded elements).

[0001] The invention relates to premium threaded tubular connectionscomprising at least one set of metal-metal sealing surfaces and makeupabutments on male and female elements that make up the threadedconnection, the threaded elements being formed at the end of a tubularcomponent of a great-length pipe or short (coupling) type.

[0002] Many types of threaded tubular connections are known, primarilyused to constitute casing strings or tubing strings or drillpipe stringsfor hydrocarbon or the like wells, such as geothermal wells.

[0003] Threaded tubular connections are also known on riser columns forconnecting sea bottom wells to offshore production platforms.

[0004] Such threaded tubular connections are subjected to a variety ofoverall stresses (axial tension or compression, internal or externalfluid pressure, bending, torsion), which may be combined (for exampleaxial tension+internal pressure), possibly with fluctuating intensity.

[0005] Premium threaded tubular connections not only have to resistrupture but must also remain tightly sealed, in particular to gas,despite such stresses that may be combined and despite tough on-siteservice conditions.

[0006] The stresses may change in nature as the pipes are lowered intothe well or during operation; as an example, tensile stresses maybriefly change into compressive stresses.

[0007] Threaded connections must also be capable of being made up andbroken out many times without degradation in performance, in particularby galling.

[0008] After breakout, the tubular components can be re-used in otherwells under different service conditions.

[0009] French patent FR 1 489 013 and European patent EP 0 488 912describe examples of such premium threaded tubular connections, inparticular for a threaded and coupled connection with two great-lengthpipes joined via a threaded coupling.

[0010] U.S. Pat. No. 5 687 999 and U.S. Pat. No. 4,494,777 describeother examples of an integral premium threaded tubular connectiondirectly connecting two great-length pipes.

[0011] The threaded tubular connections described in FR 1 489 013, EP 0488 912 and U.S. Pat. No. 4,494,777 have a front axial abutment surfaceat the free end of at least one of the threaded elements, generally themale element, and a sealing surface on a peripheral surface of athreaded element immediately adjacent the front surface of the samethreaded element.

[0012] The portion of the threaded element between the first thread ofthe threading and the front axial abutment surface at the free end isgenerally termed a lip.

[0013] In many premium threaded connections and in particular for thelast three cited patents, the male sealing surface is located at the endof the male lip, which varies in length depending on the threadedconnections.

[0014] When a premium threaded tubular connection is made up into themade-up position, the axial abutments are in contact pressure to createa reaction equal to a given makeup torque T_(m).

[0015] The corresponding male and female sealing surfaces then exhibitradial interference generating a contact pressure and the thread flankstermed “load flanks” located on the thread on the side opposite the freeend of the threaded element are in contact under contact pressure,placing the lip under axial compression.

[0016] The interfering sealing surfaces can cause problems with gallingduring make up if they have an unsuitable geometry. They can also runthe risk of leaking in service if the contact pressure, and inparticular the integrated contact pressure over the active width of thesealing surfaces, is insufficient.

[0017] To avoid the risk of leaking, the integrated contact pressuremust remain above a certain value expressed in N/mm; for a givengeometry, this integrated contact pressure is a function of the relativepositioning of the elements at the end of makeup and the servicestresses.

[0018] It is particularly difficult to obtain a threaded tubularconnection that resists, in a manner equivalent to a pipe, the differentstresses in service and which remains gas tight under such stresses, thestress after makeup being modified by the application of externalstresses in service, for example axial tension or compression, bending,internal or external pressure.

[0019] We have sought to develop a premium threaded tubular connectionwith an axial abutment located at the free end of the lip of at leastone threaded element that has a maximum resistance to leakage when thethreaded connection is subjected to high internal or external pressuresand that preserves such resistance to leakage when the threadedconnection is subjected to a high external tensile force, which tensileforce tends to separate the corresponding abutment surfaces axially, andin particular the sealing surfaces.

[0020] The tensile force can originate from axial or bending tensilestresses. The terms “tensile force” or “tensile load” as used in theremainder of the present document means the set of external stressesthat subjects all or a portion of the threaded tubular connection tosuch stresses or loads.

[0021] Such a threaded tubular connection can be characterized by thevariation in the integral of the contact pressure between the sealingsurfaces over their width (or integrated contact pressure) as a functionof the tensile load, expressed as a % of the load corresponding to theyield strength of the pipes in the string.

[0022] We have also sought to minimize the risks of galling on makeup ofthe threaded tubular connection.

[0023] We have also sought to provide an invention that advantageouslyapplies to a threaded connection comprising at least two axialabutments, one of which is external and the other, internal.

[0024] We have also sought to provide a threaded connection that caneasily be made up on-site.

[0025] We have also sought to provide theoretical sealing performancesfor the threaded connection that are not susceptible of beingsignificantly reduced due to difficult on-site operating conditions.

[0026] The threaded connection of the invention comprises firstly, inknown manner, a male threaded element at the end of a first tubularcomponent and a female threaded element at the end of a second tubularcomponent.

[0027] The male threaded element comprises a male threading, at leastone male sealing surface on the external peripheral surface and at leastone male surface on the axial abutment.

[0028] The female threaded element correspondingly comprises a femalethreading, at least one female sealing surface on its internalperipheral surface and at least one female axial abutment surface.

[0029] The male threading is made up into the female threading until atleast one male axial abutment surface abuttingly co-operates, producinga reaction to the makeup torque with the corresponding female axialabutment surface, each male sealing surface then interfering with thecorresponding female sealing surface.

[0030] On at least one threaded element, an abutment surface in abutmentreaction among the abutment surface or surfaces is produced on the frontsurface of the free end of the threaded element and is termed the distalaxial abutment surface.

[0031] A lip separates the distal axial abutment surface from thethreading on the threaded element under consideration, one sealingsurface termed the “lip sealing surface” being disposed on this lip at agiven axial distance from the end of the threading.

[0032] The lip is thus subjected to axial compressive loads resultingfrom the distal axial abutment surface abutting in abutment reactionwith the corresponding axial abutment surface.

[0033] In accordance with the characterizing feature of the invention,the lip comprises a portion termed the “appendix” between the lipsealing surface and the distal axial abutment surface at the free end ofthe lip.

[0034] This appendix can produce a lip that has both high radialstiffness and low axial stiffness.

[0035] U.S. Pat. No. 4,624,488 and U.S. Pat. No. 4,795,200 describethreaded connections with an appendix between a sealing surface and afront surface of the free end of a threaded element.

[0036] However, neither of these two patents discloses a front surfaceof the free end as an abutment surface in reactive abutment to themakeup torque, and the appendix does not carry out the same set offunctions.

[0037] The appendix in Ferguson (U.S. Pat. No. 4,624,488) providesprotection against damage resulting from knocks during on-sitemanipulation and increases the ultimate tensile strength of the threadedconnection under axial tension.

[0038] In addition the appendix in Tung (U.S. Pat. No. 4,795,200) canincrease the radial stiffness of the lip on a threaded connectionwithout the distal axial abutment surface, thus increasing the contactpressure at the sealing surfaces on this threaded connection.

[0039] Firstly, the inventors have noted that the appendix of thepresent invention also increases the radial stiffness of the lip on athreaded tubular connection with a distal axial abutment surface andthat this increase in stiffness results for a premium threaded tubularconnection, in an increase in the effective axial contact width of thesealing surface on the lip and in the integrated contact pressure onthis distal axial abutment width.

[0040] Such an increase is not obvious compared with the teaching of theTung patent as axial compression of the lip generally tends to “banana”or bow the lip and would reduce the effective contact width of thesealing surfaces and the integrated contact pressure.

[0041] The inventors have also noted that, non obviously, the increasein the radial stiffness due to the appendix also results, for a premiumthreaded tubular connection of the invention, in an increase in theeffective radial contact width of the distal axial abutment surface andin the integrated contact pressure over the radial width of this distalaxial abutment surface.

[0042] Such an effect cannot be known or deduced from the Tung patent,which does not consider such distal axial abutment surfaces.

[0043] The inventors have also noted a further non obvious effect of theappendix on the threaded tubular connection of the invention.

[0044] The appendix reduces the axial stiffness of the lip and as aresult, increases the elastic deformation of the lip at constant axialcompressive stress.

[0045] When a tensile load is exerted on the threaded connection, thisincreased elastic deformation can shift the detachment of the abutmentand especially the critical value of the integrated contact pressureover the width of the lip sealing surface towards relatively hightensile loads.

[0046] Here again, such an effect could not be discovered or deduced inan obvious manner from the Tung patent, which does not consider threadedtubular connections provided with a distal abutting sealing surface andwhich does not consider the risks of leakage under tensile stresses.

[0047] Further beneficial effects and advantages of the appendix on thepremium threaded tubular connection of the invention can be deduced fromthe particular embodiments of the invention that are discussed below.

[0048] On the lip sealing surface side, the appendix can be bordered byany peripheral surface, but a substantially cylindrical peripheralsurface is preferred to maximize the radial thickness of the distalaxial abutment surface.

[0049] Preferably, the axial length of the appendix is in the range 8%to 75% of the total length of the lip, and more particularly between 20%and 60% thereof.

[0050] Preferably, the ratio of the axial length of the appendix to theradial thickness of the distal axial abutment surface is less than 3.

[0051] Advantageously, each lip sealing surface is a surface selectedfrom the group formed by conical, toric or complex surfaces comprising acombination of conical surfaces, cylindrical surfaces and/or one or moretoric surfaces.

[0052] Highly advantageously, one or at least one lip sealing surface isa complex surface comprising two surface portions that are mutuallytangential, namely a conical portion located on the side of the distalaxial abutment surface and a toric surface with a large radius, forexample with a radius of more than 20 mm, located on the threading side,the corresponding sealing surface on the other threaded element being aconical surface with a substantially identical taper to that of theconical portion of the lip sealing surface and with an axial widthadapted to the total axial width of the lip sealing surface.

[0053] Independently of the presence or otherwise of an appendix, such acomplex surface configuration can increase the integrated contactpressure over the width of the lip sealing surface.

[0054] Highly preferably, the mean inclination of each lip sealingsurface is at least 10° with respect to the axis of the threadedconnection.

[0055] Highly preferably, the axial width of the lip sealing surface is10 mm or less, preferably 5 mm or less.

[0056] Preferably, the distal axial abutment surface is a planar surfaceperpendicular to the axis of the threaded connection or a conicalsurface coaxial with the threaded connection with an apex half angle inthe range 70° to 90°, which in the latter case tends to encouragecontact between the lip sealing surface and the corresponding sealingsurface.

[0057] The accompanying figures illustrate certain embodiments of theinvention which will now be described in detail.

[0058]FIG. 1 shows a half axial cross section of a prior art threadedand coupled tubular connection.

[0059]FIG. 2 shows a half axial cross section of a threaded and coupledtubular connection of the invention.

[0060]FIG. 3 shows a half axial cross section of an integral threadedtubular connection for a riser in accordance with the invention.

[0061]FIG. 4 shows a half axial cross section of an integral threadedtubular connection in accordance with the invention, termed a “flush”connection, i.e., with no change in the external or internal diameter atthe threaded tubular connection.

[0062]FIG. 5 is an enlargement of the free end of the male threadedelement of FIG. 2.

[0063]FIG. 6 shows the free end of FIG. 5 after makeup with thecorresponding female portions.

[0064]FIG. 7 shows an enlargement of the free end of the male threadedelement of FIG. 3.

[0065]FIG. 8 diagrammatically shows the free end of the male threadedelement of FIG. 1 (prior art).

[0066] FIGS. 9 to 11 diagrammatically show three variations of the priorart free end of FIG. 8.

[0067]FIG. 12 shows a graph of the contact width and integrated contactpressure over this width at the distal axial abutment surface and of thelip sealing surface as a function of the axial tensile load exerted onthe threaded tubular connection of FIG. 1 (prior art).

[0068]FIG. 13 shows the same graph for the threaded tubular connectionof the invention of FIG. 2.

[0069]FIG. 14 diagrammatically shows a few male threads coupled with afew female threads on the threaded tubular connection of FIG. 2.

[0070]FIGS. 15, 16 and 17 diagrammatically show the dispositions of thethreaded elements during engagement of these elements before makeup inthe case of radial (FIGS. 15, 16) or angular (FIG. 17) misalignment.

[0071]FIG. 1 shows a prior art threaded and coupled tubular connection200 between two pipes 101, 101′, which are great-length pipes, via acoupling 202 which is a short-length tubular component.

[0072] The term “pipe” or “great-length tubular component” means pipesseveral meters long, for example about 10 m long.

[0073] Connections 200 are routinely used to produce casing or tubingstrings for hydrocarbon wells, risers or for drillpipe strings for saidwells.

[0074] The pipes can be produced from any type of non alloyed, lightalloy or heavy alloy steel or even from heat treated or cold-workedferrous or non ferrous alloys depending on the service conditions suchas: mechanical stress level, corrosive nature of the fluid internal toor externally of the pipes.

[0075] It is also possible to use steel tubes with low corrosionresistance provided with a coating, for example of synthetic materialpreventing any contact between the steel and the corrosive fluid.

[0076] The ends of pipes 101, 101′ are provided with identical maleelements 1, 1′ and are coupled via a coupling 202 provided with a femalethreaded element 2, 2′ at each end.

[0077] The male threaded elements 1, 1′ are respectively connected bymaking up into female threaded elements 2, 2′ to constitute twosymmetrical threaded connections 100, 100′ connected by a lug 10 severalcentimeters long.

[0078] Lug 10 of the coupling has an internal diameter that issubstantially identical to that of the end of pipes 101, 101′ so thatthe flow of internal fluid is not disturbed.

[0079] The threaded tubular connections 100, 100′ are symmetrical, andso the function of only one of these connections needs to be described,for example threaded tubular connection 100.

[0080] Male threaded element 1 comprises a male threading 3 withtrapezoidal threads of the type known as “buttress” threads as definedin API specification 5B (API=American Petroleum Institute); this malethreading 3 is tapered and disposed on the outside of the male elementand is separated from the free end 7 of said element by a non threadedlip 11. The free end 7 constitutes an annular surface with an axialabutment termed a distal axial abutment surface disposed substantiallytransversely.

[0081] Next to the free end 7 on the external surface of lip 11 is aconical surface 5 forming a male lip sealing surface; its taper isgreater than that of the male threading 3.

[0082] The female element 2 comprises means that mate with those of maleelement 1, i.e., they match in terms of their shape and are arranged toco-operate by their disposition on the female threaded element with themale means on the male threaded element.

[0083] Female element 2 comprises an internal tapered female threading 4and a non threaded portion between the threading and the lug 10.

[0084] This non threaded portion comprises an annular axial abutmentsurface 8 with a substantially transverse orientation forming a shoulderat the end of the lug and a conical surface 6 forming a female sealingsurface immediately adjacent to the shoulder on the threading side 4.

[0085] After complete makeup of the male threading in the femalethreading, abutment surfaces 7 and 8 bear against each other whilebearing surfaces 5, 6 radially interfere and are thus under metal-metalcontact pressure. Surfaces 5, 6 then constitute metal-metal sealingsurfaces that aim at rendering the threaded connection tight even tohigh internal or external fluid pressures, against gaseous fluids andfor various stresses (axial tension, axial compression, bending, torsion. . . ), simple or combined, static or fluctuating.

[0086] Such threaded connections are termed premium connections due totheir performances compared with standard threaded tubular connectionssuch as those defined by API specification 5CT.

[0087] Threaded tubular connections such as 100 in FIG. 1 must, however,accommodate contradictory geometrical imperatives explained in FIGS. 8to 10.

[0088] The length and thickness of the lip at the lip sealing surfacemust be sufficient to obtain a given radial stiffness in the lip, whichbehaves like a spring (see FIG. 8); the contact pressure for a givenradial interference then varies with the radial stiffness of lip 11.

[0089] However, when the threaded connection is subjected to an internalor external fluid pressure, the lip bends, which induces a mismatch inthe angles of the sealing surfaces 5 and 6 and thus, a reduction in theeffective contact width and of the integrated contact pressure. Bendingof the lip due to fluid pressure is greater when the portion of lip 35between the start of threading 3 and the lip sealing surface 5 is long.

[0090] If, for reasons that will be given below, the length l_(t1) is tobe increased to a length l_(t2) (FIG. 10) by increasing the abutmentlength (l_(s3)>l_(s1)), which avoids increasing the length of portion 35of lip 11, the radial thickness e₂ of the distal axial abutment surface7 becomes insufficient to ensure a sufficient value of the makeup torqueto prevent undesirable breakout of the threaded tubular connection.

[0091] To overcome this disadvantage, the end of the lip can be taperedbefore machining the abutment 5 so that the internal peripheral surfacehas a smaller diameter (FIG. 11) towards its end; such a tapering,however, necessitates a further machining operation.

[0092] To overcome the disadvantage indicated with respect to FIG. 10,the taper of the lip sealing surface 5 (angle B<angle A=see FIG. 9) canbe reduced but such a configuration leads to a large amount of frictionof the bearing surfaces 5, 6 at the end of makeup from the moment atwhich they interfere; this results in high galling risks, in particularfor certain types of materials (high Cr steels, Ni alloys . . . ).

[0093]FIG. 2 shows a threaded tubular connection of the inventiondirectly derived from that of FIG. 1 in particular by modifying thestructure of the lip 11, which comprises an appendix 13, the structureof the female threaded element being adapted as a result by returningthe female axial abutment surface towards the center of coupling 202;the axial length of lug 10 in FIG. 2 is shorter than in FIG. 1.

[0094]FIG. 5 shows a detail of the male lip 11 of the threadedconnection of FIG. 2.

[0095] In FIG. 5, male lip 11 with total length l_(t) comprises a lipsealing surface 5 with a total axial width l_(s) which is separated fromthe distal axial abutment surface 7 by an appendix 13 with an axiallength l_(a).

[0096] The distal axial abutment surface 7 is a concave conical surface,coaxial with the threaded connection and with an apex half-angle of 75°(angle of 15° with respect to the normal to the axis). Such adisposition is known to increase the contact pressure between thesealing surfaces 5, 6 on threaded connections of the type shown in FIG.1.

[0097] Appendix 13 has an external cylindrical peripheral surface 19,which is connected to the distal axial abutment surface 7 by a toricsurface with a low radius R4.

[0098] The axial length of appendix l_(a) shown in FIG. 5 is about 25%of the total axial length of the lip l_(t), these distances being takenwith respect to the point of intersection of surfaces 7 and 19.

[0099] The ratio between the axial length of appendix l_(a) and theradial thickness e_(b) of the distal axial abutment surface is about0.9. Too high a ratio of more than 3 risks causing buckling of theappendix.

[0100] The lip sealing surface 5 is a complex surface that is inclinedto the axis (mean inclination of 15°) and is connected to appendix 13 bya toric surface with a low radius of curvature R3 and to the lip on thethreading side by a further toric surface with a low radius of curvatureR2.

[0101] R3, R4, for example, are of the order of 0.5 to 1 mm; R2 is ofthe order of 5 mm.

[0102] The lip sealing surface 5 is constituted by:

[0103] a) on the free end side 7, a conical portion 33 with a taper of50% (i.e., an inclination of 14° to the axis) with a width l_(c) of theorder of 1.5 mm, for example; and

[0104] b) on the threading side, a toric portion 31 with a large radiusof curvature R1 (for example 60 mm), with a width l_(r) (for example 1.5mm) which is tangential to the toric portion 33.

[0105] This enables to obtain a lip sealing surface which is short(width l_(s) close to 3 mm) and that is much more inclined to the axisthan the threading (taper 6.25%, i.e., an inclination of 1.8° to theaxis), and then to minimize the risks of galling of the sealing surfacesduring makeup. The moment of first contact between the sealing surfaceson makeup is delayed and the helical frictional length from this firstcontact is reduced.

[0106] The conical+large radius of curvature toric geometricalconfiguration on the threading side enables to obtain a stable contactas regards the width between sealing surfaces 5, 6 while the radialinterference between the sealing surfaces 5, 6 and/or tapered threadings3, 4 and the application of internal fluid pressure tends to “banana”lip 11 and slightly change the inclination of the male sealing surfaceby a fraction of a degree. Such a variation in the inclination tends tosubstantially reduce the effective contact width and the integratedcontact pressure over the abutment width at the conical sealingsurfaces.

[0107] The existence of a toric portion with a large radius of curvatureR1 on the threading side (R1 is preferably between 30 and 120 mm, in thepresent case 60 mm) enables to preserve the advantages of a conicalbearing surface under service conditions (functional stability of thisabutment).

[0108]FIG. 6 shows the co-operation of the means disposed on the malelip 11 and on the corresponding female portion in the made up position.

[0109] The female threaded element comprises a female axial abutmentsurface 8 which is convexly conical, with an apex half angle that isequal or substantially equal to that of the distal surface 7 and whichforms a shoulder.

[0110] At the bottom of this shoulder, at an axial distance from thefemale axial abutment surface and facing the male sealing surface 5 is aconical female sealing surface 6 with a taper equal to that of theconical portion 33 of the male lip sealing surface 5.

[0111] The axial width of the female sealing surface 6 is close to thetotal axial width l_(s) of the lip sealing surface 5 and is thus adaptedfor stable operation of these sealing surfaces in service.

[0112] The internal peripheral surface of the female threaded elementbetween the female sealing surface 6 and the female axial abutmentsurface can be of any shape since it does not radially interfere withthe external peripheral surface 19 facing the appendix 13.

[0113] A short radius is provided to connect this female peripheralsurface to the female axial abutment surface 8.

[0114] Firstly, it should be noted that the location of the sealingsurface 5 away from the free end of the lip limits bending of the lipwhen the threaded connection is subjected to internal or externalpressure of a fluid and thus limits the reduction in effective contactwidth and that of the integrated contact pressure between sealingsurfaces 5, 6 for threaded connections subjected to such internal orexternal pressures, in particular internal pressures.

[0115] The graphs shown in FIG. 12 and 13 illustrate a distinctadvantage of the threaded connection of the invention of the type shownin FIG. 2 (FIG. 13) compared with a similar prior art threadedconnection of FIG. 1 (FIG. 12).

[0116] The prior art threaded connection studied corresponds to a VAMTOP® premium threaded tubular connection as shown in VAM® catalogue n°940 edited by Vallourec Oil & Gas in July 1994 for pipes with anexternal diameter of 244.48 mm and thickness 13.84 mm (9⅝″×53.5 lbft),grade L80 (minimum yield strength 551 MPa).

[0117] The threaded tubular connection of the invention has beenmodified simply by adding an appendix with an axial length of 3 mm(l_(a)=25% 1 _(t)): see FIG. 5.

[0118] Using the finished elements analysis method (FEA), we calculatedthe variation in effective contact width and the integrated contactpressure over this width for abutment surfaces 7, 8 and for bearingsurfaces 5, 6 on a threaded connection made up to the nominal makeuptorque as a function of the axial tensile load to which the threadedconnection is subjected, expressed as a % of the load corresponding tothe pipe body yield strength (PBYS).

[0119] Regarding the abutment surfaces 7, 8, we see that the effectivecontact width (curve A), initially 3.8 mm, reduces very rapidly andfalls to 0 for a load corresponding to 42% PBYS. Above this load, theabutment surfaces are no longer in contact. The integrated contactpressure between the abutment surfaces (curve B) follows the sameprofile (initial value 770 N/mm).

[0120] Curve C relating to the change in the contact width between thesealing surfaces indicates an effective contact width reducing from 1.5to 1.1 mm when the axial tensile load changes from 0 to 100%.

[0121] This small variation in effective contact width is sufficient tocause the integrated contact pressure to fall from 700 N/mm to 300 N/mmfor the same variation in axial tensile load (curve D).

[0122] Users have for some time considered that a risk of leakage inservice exists when the integrated contact pressure calculated forfinished elements is less than 437 N/mm (line S).

[0123] Such a threshold is exceeded for the prior art threadedconnection when the tensile load is higher than that corresponding to56% PBYS: the criterion employed, therefore, is severe.

[0124] It should be noted that the sealing surfaces in accordance withthe test geometry correspond to those of 5 and 6 in FIGS. 5 and 6(conical male sealing surface, 50% taper+toric sealing surface with 60mm radius) which are considered to improve the contact stability underload with respect to simple tapered sealing surfaces.

[0125] The same calculations were carried out for the modified threadedtubular connection of the invention which was made up to the samenominal makeup torque as the prior art threaded connection.

[0126] Curves A, B, C, D and S in FIG. 13 (threaded connection of theinvention) have the same meanings as those of FIG. 12 (prior artthreaded connection).

[0127] Curves A, B and C in FIG. 13 are similar to those of FIG. 12.

[0128] Concerning the integrated contact pressure on the abutmentsurfaces (curve B), note an integrated contact pressure slightly higherthan 30 N/mm and slightly delayed detachment of the axial abutmentsurfaces (48% PBYS compared with 42%) for the threaded connection of theinvention.

[0129] The principal difference concerns the development of theintegrated contact pressure between the sealing surfaces (curve D) whichreduces much more slowly on the threaded connection of the invention sothat the threshold of 437 N/mm (line S) is only exceeded beyond a loadcorresponding to 89% PBYS.

[0130] The criterion for the integrated contact pressure, which is astrict criterion, recently introduced by users highly concerned withguaranteeing seals on threaded connections, is satisfied for a widerange of service conditions for the threaded connection of theinvention.

[0131] The low axial stiffness of lip 11 resulting from the presence ofappendix 13 contributes to the better performance of the threadedconnections of the invention as regards sealing under tension.

[0132] This low axial stiffness induces firstly, a favorable increase inradial stiffness for the seal performance of the threaded connection.

[0133] The low axial stiffness can also allow the lip at the end ofmakeup to store a large compression in axial deformation, whichdeformation can then advantageously be restored when the threadedconnection is subjected to axial tensile loads.

[0134] Too short an appendix (l_(a)<8% 1 _(t)) does not cause asufficient gain in the sealing characteristics under tensile load.

[0135] Too long an appendix (l_(a)<75% 1 _(t)) risks causing buckling ofthe lip and a reduction in the sealing performances.

[0136] The lip and associated means (5, 7, 13) are also relatively easyto produce by machining.

[0137] Other advantages can result from the low axial stiffness of thelip of the threaded connection of the invention.

[0138] A first additional advantage concerns the precision of the realmakeup torque.

[0139] Threaded connections are generally made up into position usingmechanical or hydraulic machines termed “power tongs” which developlarge torques as they have to make up the threaded connection beyondcontact of the axial abutment surfaces.

[0140] These tongs stop when a given makeup torque has been reached(nominal torque).

[0141] However, because of the inertia of the tongs, the real torqueobtained may differ from the desired nominal torque.

[0142] This difference depends on a number of factors and can be reducedby reducing the rate of makeup, which affects the makeup productivity.

[0143] The reduction in the axial stiffness of the lip in the threadedconnection of the invention enables to obtain a torque rise curve thatis more shallow between contact and the final make up position and thusenables either to reduce the difference between the nominal torque andthe real makeup torque, or to allow faster makeup.

[0144] A further additional advantage concerns the behavior of athreaded tubular connection under axial compressive load.

[0145]FIG. 14 illustrates the appearance of male and female trapezoidalthreads 21 and 22 respectively in a threaded connection with taperedthreadings made up into position.

[0146] Male threads 21 have a thread crest 29, a thread root 27 bothinclined at an angle C (for example 1.8°) to the axis, a load flank 23and a stabbing flank 25.

[0147] The female threads 22 also have a thread crest 28, a thread root30, a load flank 24 and a stabbing flank 26.

[0148] Because of the reaction on the abutment surfaces 7, 8, the maleload flanks 23 and female load flanks 24 are in contact while thestabbing flanks 25, 26 exhibit a clearance d₁.

[0149] Because of the taper of the threadings (angle of inclination C),the female thread crests 28 radially interfere with the male threadroots 27, while a clearance d₂ exists between the male thread crests 29and female thread roots 30.

[0150] When the threaded connection is subjected to axial compressiveloads, the load flanks 23, 24, which are initially in contact, detachand all of the compressive loads are then supported by the axialabutment surfaces 7, 8 in addition to the compressive stresses resultingfrom makeup. If the equivalent Von Mises stresses then exceed the yieldstrength, plasticising occurs and then there is a risk of leakage and/orgalling after breakout and further makeup.

[0151] A low axial lip stiffness allows the stabbing flanks 25, 26 tocome into contact, which then take up the axial compressive loads beforethe equivalent stress on the abutment exceeds the yield strength.

[0152] The threaded connection of the invention thus has excellentmechanical strength in axial compression.

[0153]FIG. 3 shows a further type of threaded tubular connection of theinvention, for work-over risers.

[0154] Threaded connection 300 is of the integral type, male threadedelement 1 being formed at the end of a first pipe 101 and femalethreaded element 2 being formed at the end of a second pipe 102 bymachining the pipes.

[0155] Alternatively, the threaded elements 1 and 2 may result from thethickening of the pipe ends by upsetting (increase in the externaldiameter and/or decrease in the internal diameter).

[0156] Alternatively again the male and female elements can be connectedto the pipes, for example by welding.

[0157] This type of threaded connection comprises two pairs of axialabutment surfaces, each pair comprising a distal axial abutment surface.

[0158] A first pair, the “internal abutment” pair, is constituted asbefore by a distal surface 7 at the free end of the male threadedelement 1 and an annular surface 8 forming a shoulder on the femalethreaded element 2.

[0159] The other pair, the “external abutment” pair, is symmetricallyconstituted by a distal surface 18 at the free end of the femalethreaded element 2 and an annular surface 17 forming a shoulder on themale threaded element 1.

[0160] All four axial abutment surfaces are planar, perpendicular to theaxis of threaded connection 300.

[0161] A lip 11, 12 separates each abutment from the threadings.

[0162] Female lip 12 does not have a sealing surface.

[0163] Male lip 11 (see FIG. 7) comprises a lip sealing surface 5axially separated from the distal axial abutment surface 7 via anappendix 13.

[0164] Sealing surface 5 is a complex surface constituted on the freeend side by a conical portion 33 inclined at 50% and on the threadingside 3 by a toric portion 31 with radius R1 (40 mm) tangential to theconical portion 33, the female sealing surface 6 simply being conicalwith a taper of 50% and with an axial width that is adapted to the totalwidth of the male sealing surface 5.

[0165] The appendix 13 has an external peripheral surface 19 with acylindrical shape and with an axial length l_(a) of 5 mm, representingabout 9% of the total axial length l_(t) of the lip.

[0166] The ratio of the axial length of the appendix to the radialthickness of the distal axial abutment surface is about 0.75.

[0167] The portion of the lip located between the lip sealing surface 5and the threading 3 comprises, on its external peripheral surface 35,two cylindrical surfaces 37 and 39, the surface 39 starting at thethreading root 3 having a smaller diameter D2 than the surface 37 on thesealing surface side (diameter D1), where (D2−D1) is about 1 mm.

[0168] Such a step increases the radial stiffness of the lip sealingsurface 5 and thus the contact pressures between the sealing surfaces 5,6. It also reduces the “banana” deformation of the lip when the threadedconnection 300 is subjected to internal fluid pressure. It alsocontributes, in combination with the appendix 13, to protecting sealingsurface 5 from signs of damage in the case of misalignment on engagingthe threaded elements.

[0169] The following table 1 compares the integrated contact pressuresfor 2 threaded connections for work over risers for pipes with anexternal diameter of 219.08 mm (8⅝″) and 17.8 mm thickness, grade P110(minimum yield strength 758 MPa) without an appendix 13 (prior art) andwith an appendix 13 (in accordance with the invention).

[0170] At the end of makeup, surfaces 17, 18 of the external abutmentare the first to come into contact (primary abutment), makeup beingcontinued until the surfaces 7, 8 of the internal abutment come undercontact pressure (secondary abutment).

[0171] Table 1 shows values for the integrated contact pressures overthe contact width at the sealing surfaces, obtained by numericalcalculation at the end of makeup and under axial tension. TABLE 1Integrated contact pressure between sealing surfaces Integrated contactpressure (N/mm) Threaded connection Prior art threaded in accordancewith connection invention (FIG. 3) at end of makeup 1286 1523 makeup +80% PBYS 1214 1462 makeup + 100% PBYS 1188 1442

[0172] The integrated contact pressures were higher and increased alittle more slowly with the threaded connection of the invention forthis configuration, with first contact between the external abutmentsurfaces. The appendix with a very limited length (9% of the total liplength) and lip 11 were very stiff radially (10 mm thickness at step37), and so the differences compared with the prior art threadedconnection were lower than in the preceding example (VAM TOP®).

[0173] For the threaded connection 300 of FIG. 3, FIGS. 15, 16 and. 17show the limiting conditions for engagement of the threaded elements inthe presence of the appendix 13.

[0174]FIG. 15 shows the maximum possible radial misalignment d3 whenengagement of the threaded elements 1 and 2 commences, the male lipsealing surface 5 coming into contact with the female free end 18: d3can exceed 10 mm for the threaded connection 300 with the dimensionsgiven above.

[0175]FIG. 16 shows the maximum possible radial misalignment d4 a littlelater when the male lip sealing surface 5 comes into contact with thefirst female thread: d4 is about 8 mm for the threaded connection underconsideration.

[0176]FIG. 17 shows the maximum possible angular misalignment E, themale lip sealing surface 5 being in contact with the female threadingand the male and female threads not yet being engaged: E is about 4°.

[0177] These values of d3, d4 and E are higher than in the absence ofappendix 13. The threaded connections of the invention thus bettertolerate improper engagement conditions of the threaded elements.

[0178] Of course appendix 13 protects the lip sealing surface 5 fromaxial end shocks during on-site manipulation.

[0179] It should be noted that in the case of FIG. 17, the appendix alsocreates a protection or radial barrier for the conical portion 33 of thelip sealing surface, which is the most critical portion as regardssealing.

[0180] The whole of the sealing surface can also be protected if, asshown in FIG. 5, the axial length l_(a) of appendix 13 is such that thelip sealing surface 5 is located on the threaded element side withrespect to the straight line D1 passing through the crest of the firstmale thread and which is tangential to the free end of the threadedelement. The straight line D1 constitutes, for example, the generatrixof the female thread crests in FIG. 17.

[0181]FIG. 4 shows an integral threaded connection 400 known as a flushconnection with a constant internal and external diameter, with internalabutment surfaces (7, 8) and external abutment surfaces (17, 18) andwith 2 pairs of sealing surfaces: an internal pair (5, 6) and anexternal pair (15, 16).

[0182] Threaded connection 400 is sealed both to external pressures bymeans of the external pair of sealing surfaces and to internal pressuresby means of the internal pair of sealing surfaces.

[0183] The male sealing surface 5 of the internal pair and the femalesealing surface 16 of the external pair are lip sealing surfaces.

[0184] They are separated from the distal axial abutment surfaces 7, 18on the threaded elements on which they are formed by an appendix 13, 14.

[0185] These appendices 13, 14 can reduce the axial stiffness of lips11, 12 and render the radial stiffness of these lips a maximum.

[0186] This can maximize the sealing performances of the threadedconnection both to external fluids and to internal fluids even under arelatively high axial tension.

[0187] The mechanical behavior under compression is also improved.

[0188] The low axial stiffness of lips 11, 12 allows makeup to becontinued sufficiently after first contact of one internal or externalabutment pair, preferably internal pair, until axial abutting contact ofthe second pair of abutting surfaces.

[0189] The delay in detachment of the abutting surfaces under axialtension also enables to a certain extent to prevent or in any case tolimit the jarring of these surfaces in the case of a fluctuating tensileor bending load, such jarring being an initiating source for fatiguecracks by the phenomenon known as “fretting corrosion”.

[0190] The present invention is not limited to the threaded tubularconnections that have just been described.

[0191] It is applicable to any type of threaded tubular connection, inparticular with conical or cylindrical threadings, with one or morethreaded portions which may or may not be stepped, with trapezoidal ortriangular threads, or with wedge threads with a variable pitch orwidth.

1-19. (Canceled).
 20. A threaded tubular connection comprising: a malethreaded element at an end of a first tubular component and a femalethreaded element at an end of a second tubular component, the malethreaded element comprising a male threading, at least one male sealingsurface on its external peripheral surface, and at least one male axialabutment surface, the female threaded element correspondingly comprisinga female threading, at least one female sealing surface on its internalperipheral surface, and at least one female axial abutment surface, themale threading being made up into the female threading until at leastone male axial abutment surface co-operates with the correspondingfemale axial abutment surface to produce an abutting reaction againstmakeup torque, each male sealing surface then interfering radially witha corresponding female sealing surface, at least one threaded elementhaving a distal axial abutment surface among the axial abutment surfaceor surfaces producing an abutting reaction, formed on a front surface ofthe free end of the threaded element, a lip separating the distal axialabutment surface from the threading on the threaded element underconsideration, one lip sealing surface being disposed on the lip at agiven axial distance from the end of the threading, wherein the lipcomprises between the distal axial abutment surface and the lip sealingsurface an appendix comprising two peripheral surfaces to increaseradial stiffness of the lip and to reduce axial stiffness of the lipwith regard to a similar threaded tubular connection without anappendix.
 21. A threaded tubular connection according to claim 20,wherein the distal axial abutment surface at an end of the appendix isdisposed on the lip to be first in contact with the axial abutmentsurface of the mating threaded element during makeup.
 22. A threadedtubular connection according to claim 20, wherein a peripheral surfaceof the appendix located on the lip sealing surface side shows a lack ofinterfering contact with the mating threaded element.
 23. A threadedtubular connection according to claim 20, wherein a peripheral surfaceof the appendix located on the lip sealing surface side is asubstantially cylindrical surface.
 24. A threaded tubular connectionaccording to claim 20, wherein the distal axial abutment surface at anend of the appendix is a surface that extends between both of peripheralsurfaces of the appendix.
 25. A threaded tubular connection according toclaim 20, wherein the distal axial abutment surface at an end of theappendix is a planar surface, perpendicular to an axis of the threadedtubular connection.
 26. A threaded tubular connection according to claim20, wherein the distal axial abutment surface at an end of the appendixis conical, coaxial with the threaded tubular connection and with anapex half angle in a range 70° to 90° to encourage contact of the lipsealing surface and the corresponding sealing surface.
 27. A threadedtubular connection according to claim 20, wherein the appendix has anaxial length in a range 8% to 75% of a total axial length of the lip,preferably in the range 20% to 60% of the total axial length of the lip.28. A threaded tubular connection according to claim 20, wherein theappendix has an axial length and the distal axial abutment surface has aradial thickness such that a ratio of the axial length of the appendixto the radial thickness of the distal axial abutment surface is 3 orless.
 29. A threaded tubular connection according to claim 20, whereinan axial length of the appendix is configured so that the lip sealingsurface is located on a same side as the threaded element on which it islocated with respect to a straight line that passes through a crest of afirst thread of the threading and that is tangential to a free end ofthe threaded element, which enables to protect the lip sealing surfacefrom damage during handling of the threaded elements.
 30. A threadedtubular connection according to claim 20, wherein each lip sealingsurface is a surface selected from the group formed by conical, toric,or complex surfaces, the complex surfaces comprising combinations ofconical surfaces, cylindrical surfaces, and toric surfaces.
 31. Athreaded tubular connection according to claim 30, wherein one or atleast one lip sealing surface is a complex surface comprising twoportions of surfaces that are mutually tangential, namely a conicalportion located on a side of the distal axial abutment surface and atoric portion with a radius of more than 20 mm located on the threadingside, and wherein the corresponding sealing surface on the otherthreaded element is a conical surface with a taper that is substantiallyidentical to that of the conical portion of the lip sealing surface andwith an axial width that is adapted to the total axial width of the lipsealing surface.
 32. A threaded tubular connection according to claim30, wherein each lip sealing surface has a mean inclination of at least10° with respect to an axis of the threaded tubular connection.
 33. Athreaded tubular connection according to claim 30, wherein each lipsealing surface has an axial width of less than 10 mm and preferably 5mm or less.
 34. A threaded tubular connection according to claim 20,wherein a peripheral surface of the lip located between the lip sealingsurface and the threading comprises two generally cylindrical surfaceswith different diameters, the generally cylindrical surface with asmallest diameter being connected to a root of the threading, and thatwith a largest diameter being connected to the lip sealing surface. 35.A threaded tubular connection according to claim 20, wherein a singlethreaded element has a lip with a lip sealing surface, an appendix and adistal axial abutment surface, the other threaded element not exhibitingall of these elements.
 36. A threaded tubular connection according toclaim 35, wherein the other threaded element does not exhibit any distalaxial abutment surface nor any lip sealing surface.
 37. A threadedtubular connection according to claim 35, wherein the other threadedelement of the threaded tubular connection also exhibits a distal axialabutment surface, but not a lip sealing surface.
 38. A threaded tubularconnection according to claim 20, wherein the two threaded elements ofthe threaded tubular connection each have a lip with a lip sealingsurface, an appendix, and a distal axial abutment surface.